Carbon nanotube coated structure and associated method of fabrication

ABSTRACT

A coated structure is provided that has a highly concentrated coating of carbon nanotubes so as to provide integrated thermal emissivity, atomic oxygen (AO) shielding and tailorable conductivity to the underlying surface, such as the surface of an aerospace vehicle, a solar array, an aeronautical vehicle or the like. A method of fabricating a coated structure is also provided in which a surface is coated with a coating having a relative high concentration of carbon nanotubes that is configured to provide integrated thermal emissivity, AO shielding and tailorable conductivity to the surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S.application. Ser. No. 12/907,273, filed Oct. 19, 2010, the entirecontents of which are hereby incorporated by reference.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under FA9453-10-C-0206awarded by AFRL. The government has certain rights in this invention.

TECHNOLOGICAL FIELD

Embodiments of the present disclosure relate generally to coatedstructures and, more particularly, to structures having a carbonnanotube coating and associated methods of fabrication.

BACKGROUND

Structures may include a coating that is selected based upon theproperties provided by the coating to the coated structure. For example,space vehicles may have a carbon loaded polyimide coating, such as BlackKapton®, that provides relatively high emissivity/absorbtivity as wellas relatively high conductivity for space environment applications, suchas for space vehicles in a low earth orbit (LEO) and/or space vehiclesin a geosynchronous earth orbit (GEO). While Black Kapton® may have aconductivity that is somewhat tailorable, it would be desirable in atleast some applications for a coating, such as for a space vehicle, tohave a conductivity that is even more tailorable than those coatingsthat are commercially available.

Space vehicles, particularly those in LEO, are also subjected to theimpingement of atomic oxygen (AO), which may erode the surface of aspace vehicle if the surface is not sufficiently protected. BlackKapton® coatings cannot generally survive AO environments for anextended period since the Black Kapton® coating is eroded by the AO.While thicker coatings may be employed, the increased coating thicknessdisadvantageously increases the weight of the space vehicle withoutproviding an additional benefit.

In some instances, it would also be desirable to provide an insulativeboundary, such as the insulative polyimide surface of a space vehicle,between an electrical connection and the Black Kapton® coating so as toutilize the Black Kapton® coating as a radiator for the thermal loadsfrom the electrical connection. Insulative polyimide may not beeffectively bonded to a Black Kapton® coating since the mismatch in thecoefficients of thermal expansion will generally cause the polyimidesurface to curl.

It would therefore be desirable to provide an improved coating havingtailorable conductivity, AO properties and thermal radiative properties.In this regard, it would be desirable to provide an improved coating foraerospace vehicles or aeronautical vehicle as well as other applicationsdesirous of improved radiative properties.

BRIEF SUMMARY

A coated structure is therefore provided according to one embodimentwhich provides integrated thermal emissivity, atomic oxygen (AO)shielding and tailorable conductivity to the underlying surface, such asthe surface of an aerospace vehicle, a solar array, an aeronauticalvehicle or the like. A method of fabricating a coated structure is alsoprovided according to another embodiment in which a surface is coatedwith a coating that is configured to provide integrated thermalemissivity, AO shielding and tailorable conductivity to the surface. Assuch, the coated structure and associated method of fabrication may betailored to protect the underlying surface in various environments,including space or other high altitude environments, in which the coatedstructure is subject to sizable temperature fluctuations as well as theimpingement of AO.

In one embodiment, a coated structure is provided that includes asubstrate having a surface that is configured to be exposed totemperature fluctuations and a coating comprising at least 10% by volumeof carbon nanotubes. In this embodiment, the coating is configured toprovide an integrated thermal emissivity, AO shielding and tailorableconductivity to the surface.

The coated structure may be utilized in various applications includingin applications in which the surface comprises the surface of at leastone of an aerospace vehicle or an aeronautical vehicle that isconfigured to be exposed to temperature fluctuations between −180° C.and 150° C. and, in one embodiment, to temperature fluctuations between−200° C. and 200° C. In another embodiment, the surface upon which thecoating is disposed may be the rear surface of a solar array. Regardlessof the application, the coating of one embodiment may be configured toprovide a thermal emissivity of at least 0.9. The coating of oneembodiment may be configured to provide a conductivity of between 1Ω/square and 5e10 Ω/square. Further, the coating of one embodiment maybe configured to provide AO shielding for at least 30 days in a lowearth orbit (LEO).

In accordance with another embodiment, a coated structure is providedthat includes a substrate having a surface that is configured to beexposed to temperature fluctuations between −180° C. and 150° C. and, inone embodiment between −200° C. and 200° C. The coated structure of thisembodiment also includes a coating having a plurality of carbonnanotubes. The coating is configured to provide a thermal emissivity ofat least 0.9, a conductivity of less than 400 Ω/square and shieldingfrom atomic oxygen (AO).

In one embodiment, the surface upon which the coating is disposed is thesurface of at least one of an aerospace vehicle or an aeronauticalvehicle. In another embodiment, the surface upon which the coating isdisposed may be the rear surface of a solar array. In eitherapplication, the coating of one embodiment may include at least 10% byvolume of carbon nanotubes. The coating of one embodiment may beconfigured to provide a conductivity between 1 Ω/square and 400Ω/square. Additionally, the coating may be configured to provide AOshielding for at least 30 days in LEO.

In a further embodiment, a method of fabricating a coated structure isprovided that includes providing a substrate having a surface that isconfigured to be exposed to temperature fluctuations and disposing acoating upon the surface. The coating of this embodiment includes atleast 10% by volume of carbon nanotubes. The coating of this embodimentis also configured to provide an integrated thermal emissivity, atomicoxygen (AO) shielding and tailorable conductivity to the surface.

In one embodiment, the provision of the substrate includes the provisionof an aerospace vehicle or an aeronautical vehicle that is configured tobe exposed to temperature fluctuations between −180° C. and 150° C. Inthis embodiment, the disposition of the coating upon the surface mayinclude the disposition of the coating upon the surface of at least oneaerospace vehicle or aeronautical. In another embodiment, the provisionof the substrate may include the provision of a solar array having oneor more solar cells on one surface and an opposed rear surface uponwhich the coating is disposed. Regardless of the application, thecoating of one embodiment may be configured to provide a thermalemissivity of at least 0.9. The coating of one embodiment may beconfigured to provide a conductivity between 1 Ω/square and 5e10Ω/square. The coating of another embodiment may be configured to provideAO shielding for at least 30 days in LEO.

The features, functions and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Having thus described the disclosure in general terms, reference willnow be made to the accompanying drawings, which are not necessarilydrawn to scale, and wherein:

FIG. 1 is a perspective view of an aerospace vehicle and/or aeronauticalvehicle embodying a coated structure in accordance with one embodimentof the present disclosure;

FIG. 2 is a cross-sectional view of a portion of the aerospace vehicleof FIG. 1 illustrating the coated structure of one embodiment of thepresent disclosure;

FIG. 3 is a cross-sectional view of a solar cell array embodying acoated structure in accordance with one embodiment of the presentdisclosure; and

FIG. 4 is a flow chart illustrating operations performed duringfabrication of a coated structure in accordance with one embodiment ofthe present disclosure.

DETAILED DESCRIPTION

The present disclosure now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments are shown. Indeed, the embodiments may take many differentforms and should not be construed as limited to the embodiments setforth herein; rather, these embodiments are provided so that thisdisclosure will satisfy applicable legal requirements. Like numbersrefer to like elements throughout.

A coated structure is provided in accordance with embodiments of thepresent disclosure. As a result of the radiative properties of thecoating, the coated structure may be deployed in a variety ofapplications. For example, an aerospace vehicle 10 as shown in FIG. 1may include a coated structure in accordance with one embodiment. Oneexample of an aerospace vehicle 10 in the form of a satellite having abody 12 and a pair of solar panels 14 is depicted in FIG. 1. However, awide variety of aerospace vehicles and/or aeronautical vehicles mayinclude a coated structure of embodiments of the present disclosure suchthat the aerospace vehicle 10 of FIG. 1 should be considered by way ofan example, but not by way of limitation. Indeed, while one embodimentof an aerospace vehicle 10 includes a satellite as shown in FIG. 1,other embodiments of aerospace and/or aeronautical vehicles include highaltitude air frames, including those intended for flight high in theatmosphere.

As shown in the fragmentary cross-sectional view of FIG. 2, the externalsurface of the aerospace vehicle 10 or aeronautical vehicle may includea coated structure in accordance with one embodiment of the presentdisclosure. While the entire external surface of the aerospace vehicle10 or aeronautical vehicle may be comprised of the coated structure inone embodiment, only portions of the aerospace vehicle or aeronauticalvehicle, such as those portions of the aerospace vehicle or aeronauticalvehicle that are anticipated to not face the sun or other source ofsolar energy the coated structure, may be formed of the coated structurein other embodiments. In other words, since the coating is emissive, thecoating is typically disposed on those surfaces of aerospace vehiclesthat face the black of space and/or those surfaces that face away fromhot components, such as jet engine thermal energy or sun energy inaeronautical applications. As shown in more detail in FIG. 2, at leastthat portion of the external surface of the aerospace vehicle 10 oraeronautical vehicle that includes coated structure of embodiments ofthe present disclosure has a substrate 20 with a surface 22 and acoating 24 disposed upon the surface. For example, the substrate 20 maycomprise the air frame, the skin or other structure that defines theexternal surface of the aerospace vehicle 10 or aeronautical vehicle.The coating 24 may, in turn, be disposed upon the surface 22. While thecoating 24 may be disposed directly upon the surface 22, the coatingmay, instead, be indirectly deposited upon the surface with one or moreintermediate layers positioned between the surface and the coating. Ineither instance, however, the coating is considered to be disposed uponthe surface of the substrate. The substrate may be formed of a varietyof materials. In one embodiment, however, at least the surface of thesubstrate is formed of a polyimide.

The coating 24 that is disposed upon the surface 22 may advantageouslyinclude a high concentration of carbon nanotubes. For example, thecoating 24 of one example embodiment may include at least 10% by volumeof carbon nanotubes and, in one embodiment, at least 50% by volume ofcarbon nanotubes. In one advantageous embodiment, the coating 24 mayinclude at least 80% by volume of carbon nanotubes and, in a furtherembodiment, may include at least 90% by volume of carbon nanotubes withthe remainder of the coating comprised of other elements including, forexample, an oxide binder. The coating 24 may include eithersingle-walled carbon nanotubes or multi-walled carbon nanotubes.

As a result of the relatively high concentration of carbon nanotubeswithin the coating 24, the coating provides a number of advantageousproperties to the underlying substrate 20. In this regard, the substrate20 may be configured to be exposed to temperature fluctuations, such astemperature fluctuations between −180° C. and 150° C. for applicationsin the GEO and upper LEO. If designed more specifically for GEOapplications, the substrate 20 may be configured to be exposed totemperature fluctuations between −200° C. and +60° C. or, moreparticularly, between −180° C. and +60° C. For upper LEO applications,the substrate 20 may be configured to be exposed to temperaturefluctuations between −140° C. and +150° C. Additionally oralternatively, the substrate 20 may be configured to be exposed totemperature fluctuations between −100° C. and +200° C. for lower LEOapplications. Thus, the substrate 20 of one embodiment that is designedfor upper and lower LEO applications as well as GEO applications may beconfigured to be exposed to temperature fluctuations between −200° C.and 200° C. Further, a substrate 20 designed for aerospace applicationssuch as a high altitude airship or airplane may be configured to beexposed to temperature fluctuations between −60° C. at relative highspeeds through a portion of the atmosphere to +70° C. for enginecompartments, for example, that generate substantial internal heat.Correspondingly, the coating 24 having a relatively high concentrationof carbon nanotubes advantageously maintains its advantageousproperties, such as thermal emissivity, atomic oxygen (AO) shielding andtailorable conductivity, when exposed to these temperature fluctuations,such as between −180° C. and 150° C. and, in one embodiment, totemperature fluctuations between −200° C. and 200° C. as a result of,for example, the relatively low coefficient of thermal expansion (CTE)of the carbon nanotubes and the fact that the carbon nanotubes remain ina solid form throughout the various temperature ranges and do notundergo a phase change. Indeed, the thermal emissivity, AO shielding andconductivity of the coating 24 of one embodiment vary by no more than 5%across any one of these temperature ranges and, in one embodiment, varyby no more than 2.5%. Additionally, the coating 24 having a relativelyhigh concentration of carbon nanotubes may be relatively thin, such as 2microns or less, such that the coating and the substrate, such as apolyimide substrate, do not separate, such as by curling, when thetemperature fluctuations are experienced.

The coating 24 is configured to provide integrated thermal emissivity,atomic oxygen (AO) shielding and tailorable conductivity to the surface22 of the underlying substrate 20. In this regard, the coating may havea thermal emissivity of at least 0.9 and, in one embodiment, at least0.95, such as from 0.95 to 1.0. Coatings 24 having such high levels ofthermal emissivity are particularly useful for a number of applicationsincluding aerospace vehicles 10 or aeronautical vehicles thatadvantageously have an exterior surface with a relatively high thermalemissivity in order to protect the aerospace vehicle or aeronauticalvehicle from overheating and/or heat damage.

The coating 24 also advantageously has a conductivity that is tailorablesuch that the conductivity of the coating may be modified to mostappropriately address the particular application in which the coating isto be deployed. In this regard, the conductivity of the coating 24 maybe controllably modified by adjusting the concentration of the carbonnanotubes and/or by utilizing a different type of multi-walled carbonnanotube. The conductivity of the coating 24 may be tailored across awide range, such as from 1 Ω/square to 5e10 Ω/square. In one embodiment,the conductivity of the coating 24 is tailorable so as to have a valueof less than 400 Ω/square, such as to have a conductivity within therange of 220 Ω/square to 400 Ω/square.

The coating 24 also advantageously provides AO shielding for theunderlying surface 22. While AO shielding is of importance for a numberof different space applications, AO shielding is particularly relevantfor aerospace vehicles 10 that are intended to remain in LEO for someperiod of time since erosion due to AO is particularly problematic forLEO applications. The coating 24 may be tailored to provide differentdegrees of AO shielding. In this regard, a thinner coating 24 providessome degree of AO shielding, while a thicker coating provides increasedamounts of AO shielding. By way of example, a coating 24 having athickness of about 0.5 microns may provide AO shielding for an aerospacevehicle 10 that is anticipated to remain in LEO for about 30 days, whilea coating having a thickness of about 2 microns may provide AO shieldingfor an aerospace vehicle that is intended to remain in LEO for years.

As noted above, the substrate 20 upon which the coating 24 is disposedis configured to be exposed to a relatively wide range of temperatures.Similarly, the coating 24 is configured to continue to be thermallyemissive, to have a tailorable conductivity and to provide AO shieldingacross the same range of temperatures, such as from −180° C. to 150° C.in one embodiment and from −200° C. to 200° C. in another embodiment.Thus, the effectiveness of the coating 24 in regards to its thermalemissivity, tailorable conductivity and AO shielding is maintained andis not diminished and the coating does not otherwise suffer performancedegradation as the temperature fluctuates through these ranges.

The coating 24 may also be advantageously lightweight due to itscomposition and relative thinness. Consequently, the relativelylightweight coating 24 is advantageous for air, space and othervehicular applications since increases in weight generally add to theoperational costs.

As described above, the lightweight coating 24 provides a desirablecombination of thermal emissivity, AO shielding, conductivity andresilience to temperature fluctuations so as to protect a variety ofaerospace vehicles 10 or aeronautical vehicles. However, the coating 24may also be advantageously deployed in a number of other applications inwhich one or more of these properties is desirable. For example, thethermal emissivity of the coating 24 may be advantageously deployed inconjunction with a solar array. As shown in FIG. 3, for example, a solararray may include one or more solar cells 30 comprised of asemiconductor material configured to convert solar energy to electricalenergy and a solar panel upon which the solar cells 30 are mounted andcarried. In this regard, the solar cells 30 may be mounted to the solarpanel with a thermal adhesive 32. Although a solar panel may beconstructed in various different manners, the solar panel of oneembodiment has a honeycomb core 36 formed, for example, of aluminum withface sheets 34 disposed on opposed sides of the honeycomb core. The facesheets 34 may be formed of various materials including, for example, acomposite material formed of carbon fibers and/or Kevlar® fibersembedded in a matrix material. In this embodiment, the coating 24 ofhighly concentrated carbon nanotubes may be disposed on a surface of thesolar panel, e.g., on the rear face sheet 34, opposite the solar cells30 in order to increase the operational efficiency of the solar array.Alternatively, the solar cells 30 may be mounted on a thin flexiblesolar array substrate, such as a polyimide substrate, such that thecoating 24 is disposed on a rear surface of the substrate opposite thesolar cells. In either instance, the coating 24 is disposed on a rearsurface of the solar array opposite the solar cells 30.

As described above, the coating 24 is radiative and therefore serves toradiate the solar energy that has passed through the solar array to itsrear surface back through the solar array to increase the conversion ofsolar energy to electrical energy that is affected by the solar cells30. Solar arrays may be deployed or used in a variety of environmentsincluding space environments and other high altitude applications.However, solar arrays may be deployed in other environments if sodesired.

The coated structure including the coating 24 of embodiments of thepresent disclosure may be deployed in a number of other applications inaddition to aerospace vehicles 10, aeronautical vehicles and solararrays in order to advantageously leverage the radiative propertiesprovided by the coating. As such, the foregoing discussion regarding theuse of the coated structure in conjunction with aerospace vehicles 10,aeronautical vehicles and solar arrays is provided by way of an exampleand not as a limitation.

The coating 24 may be applied to the surface 22 of an underlyingsubstrate 20 in various manners. However, one embodiment of a method offabricating a coated structure is provided below in relation to FIG. 4.In this regard, a substrate 20 having a surface 22 that is configured tobe exposed to temperature fluctuations is initially provided as shown inblock 40. As described above, the substrate 20 may, for example, be thepolyimide exterior surface of an aerospace vehicle 10 or aeronauticalvehicle that is configured to be exposed to temperature fluctuation.Alternatively, the substrate 20 may be the rear surface of a solar arrayformed, for example by a composite face sheet 34. Alternatively, thesurface 22 of the substrate 20 may be formed of other materials, such asmetals or the like.

Regardless of its composition, the substrate 20 may be cleaned asdepicted in block 42 of FIG. 4. Thereafter, the coating 24 having a highconcentration of carbon nanotubes may be disposed on the surface 22,such as by being applied to the surface as shown in block 44. In oneembodiment, the coating 24 is sprayed onto the surface 22. Regardless ofthe manner in which the coating 24 is deposited upon the surface 22, thecoating includes a relatively high concentration of carbon nanotubessuch as at least 10% by volume of carbon nanotubes and, in oneembodiment, at least 50% by volume of carbon nanotubes. As noted above,the carbon nanotubes may be deposited upon the surface 22 in oneadvantageous embodiment such that the coating 24 includes at least 80%by volume of carbon nanotubes and, in a further embodiment, at least 90%by volume of carbon nanotubes. In order to facilitate the application ofthe coating 24, the carbon nanotubes are generally carried in a carrieror solvent, such as an alcohol solution. Once disposed upon the surface22, the carrier solvent, such as the alcohol solution, may dissolve orotherwise evaporate, such as in response to the application of heat, asshown in block 46 of FIG. 4. Following the evaporation or dissolution ofthe carrier or solvent, the carbon nanotubes remain disposed upon thesurface 22. A binder may then be applied to the carbon nanotubes inorder to further tailor the resulting properties of the coating. Seeblock 48 of FIG. 4. In this regard, the binder may be comprised of anoxide, such as silicon dioxide SiO₂ or Indium Tin Oxide (ITO), which islaid in by a variety of techniques including, for example, an ambienttechnique, such as by spraying

As described above, the resulting coating 24 maintains it propertiesover a wide range of temperatures and has a coefficient of thermalexpansion that sufficiently approximates the coefficient of thermalexpansion of the underlying substrate 20 such that the coating remainsadhered to the surface 22 of the substrate even as the temperaturefluctuates through a relatively broad range, such as between −180° C. to150° C., and, in one embodiment, between −200° C. and 200° C.Additionally, the highly concentrated carbon nanotube coating 24provides substantial thermal emissivity, tailorable conductivity and AOshielding so as to protect the underlying substrate 20 in a variety ofapplications, including space applications, such as aerospace vehiclesdeployed in LEO or GEO. Further, the relatively lightweight nature ofthe coating 24 facilitates the use of the coating in applications inwhich it is advantageous to maintain relatively low weights, such asspace applications and other vehicular applications.

Many modifications and other embodiments will come to mind to oneskilled in the art to which this disclosure pertains having the benefitof the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that thedisclosure is not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A method of fabricating an external surface ofan aerospace vehicle or an aeronautical vehicle, the method comprising:providing a substrate having a surface that is configured to be exposedto temperature fluctuations between −180° C. and 150° C.; and disposinga coating upon the surface, wherein the coating consists of: (i) aplurality of carbon nanotubes disposed on the surface of the substrateand (ii) a binder formed of silicon dioxide or indium tin oxide that islaid into the carbon nanotubes following disposition of the carbonnanotubes on the surface of the substrate, wherein the coating comprisesat least 10% by volume of carbon nanotubes, and wherein the coating isconfigured to provide to the surface a thermal emissivity, atomic oxygen(AO) shielding and tailorable conductivity while exposed to temperaturefluctuations at least between −180° C. and 150° C.
 2. A method accordingto claim 1 wherein the coating comprises at least 50% by volume ofcarbon nanotubes.
 3. A method according to claim 1 wherein the coatingcomprises at least 80% by volume of carbon nanotubes.
 4. A methodaccording to claim 1 wherein the coating comprises at least 90% byvolume of carbon nanotubes.
 5. A method according to claim 1 wherein thecoating is structured to provide a thermal emissivity of at least 0.9.6. A method according to claim 1 wherein the coating is structured tohave a tailorable conductivity up to 5e10 Ω/square while exposed totemperature fluctuations at least between −180° C. and 150° C.
 7. Amethod according to claim 1 wherein the coating has a thickness between0.5 microns and 2 microns to provide the AO shielding.
 8. A methodaccording to claim 1 wherein providing a substrate comprises providing asolar array having one or more solar cells on one surface and an opposedsurface upon which the coating is disposed.
 9. A method according toclaim 1 wherein the coating is configured to provide AO shielding for atleast 30 days in a low earth orbit (LEO).
 10. A method according toclaim 1 wherein the surface is configured to be exposed to temperaturefluctuations between −200° C. and 200° C.
 11. A method according toclaim 1 wherein the coating is configured to provide a conductivity ofbetween 1 Ω/square and 5e10 Ω/square.
 12. A method of fabricating anexternal surface of an aerospace vehicle or an aeronautical vehicle, themethod comprising: providing a substrate having a surface that isconfigured to be exposed to temperature fluctuations between −180° C.and 150° C.; and disposing a coating upon the surface, wherein thecoating consists of: (i) a plurality of carbon nanotubes disposed on thesurface of the substrate and (ii) a binder formed of silicon dioxide orindium tin oxide that is laid into the carbon nanotubes followingdisposition of the carbon nanotubes on the surface of the substrate,wherein the carbon nanotubes comprise at least 50% by volume of thecoating, wherein the coating is structured to have a tailorableconductivity up to 5e10 Ω/square while exposed to temperaturefluctuations at least between −180° C. and 150° C., wherein the coatingis also structured to provide a thermal emissivity to the surface, andwherein the coating has a thickness between 0.5 microns and 2 microns toprovide atomic oxygen (AO) shielding.
 13. A method according to claim 12wherein the coating comprises at least 80% by volume of carbonnanotubes.
 14. A method according to claim 12 wherein the coatingcomprises at least 90% by volume of carbon nanotubes.
 15. A methodaccording to claim 12 wherein the coating is structured to provide athermal emissivity of at least 0.9.
 16. A method according to claim 12wherein providing a substrate comprises providing a solar array havingone or more solar cells on one surface and an opposed surface upon whichthe coating is disposed.
 17. A method according to claim 12 wherein thecoating is configured to provide AO shielding for at least 30 days in alow earth orbit (LEO).
 18. A method according to claim 12 wherein thesurface is configured to be exposed to temperature fluctuations between−200° C. and 200° C.
 19. A method according to claim 12 wherein thecoating is configured to provide a conductivity of between 1 Ω/squareand 5e10 Ω/square.